A passive optical network (PON) is one system for providing network access over “the last mile.” The PON is a point-to-multipoint (P2MP) network comprised of an optical line terminal (OLT) at the central office, an optical distribution network (ODN), and a plurality of optical network units (ONUs) at the customer premises. PONs may also comprise remote nodes (RNs) located between the OLTs and the ONUs, for example, at the end of a road where multiple users reside. In recent years, time division multiplexing (TDM) PONs, such as Gigabit PONS (GPONs) and Ethernet PONs (EPONs), have been deployed worldwide for multimedia applications. In TDM PONs, the total capacity is shared among multiple users using a time division multiple access (TDMA) scheme, so the average bandwidth for each user is limited to well below 100 megabits per second (Mbps) for GPONs and EPONs.
As user bandwidth demands are ever increasing, ten gigabits per second (Gbps) (10 G) PONs (e.g., ten gigabit per second (Gbps) GPON (XGPONs) and 10 G EPONs) have also been standardized for next generation optical access. In TDM PON, a power splitter is used to distribute and/or collect signal to/from the ONUs. As the power splitter introduces significant loss, the performance of TDM PON is limited by the power budget. The number of users who can be served by TDM PON is typically limited to 64 and the transmission distance is limited to 20 kilometers (km). PON operators are interested in increasing the splitting ratio and a longer reach so that more users may be served and larger areas may be covered. Hence, there is a need to improve the power budget of TDM PON systems.
While the downstream power budget in TDM PON may be improved relatively easily, the upstream power budget may be more limited. For instance, the OLT may increase downstream transmit power by employing a higher power transmitter or an optical amplifier, whereas ONUs typically employ low cost lasers with low power. In addition, there is a lower loss in the downstream direction at the outside plant fiber since the downstream wavelength is in the S-band (1490 nanometers (nm) for GPON and EPON) or the L-band (1577 nm for XG-PON and 10 G EPON), whereas the upstream wavelength is in the O-band (1310 nm for GPON and EPON, 1270 nm for XG-PON and 10 G EPON). Further, the burst mode transmission used in the upstream direction introduces additional power penalty compared to the continuous mode transmissions in the downstream direction. Since ONUs are typically cost limited, it may not be practical to increase the ONUs transmit power. Consequently, there is a need in the art for methods and systems to improve the OLT receiver sensitivity in TDM PON systems.